Enzyme-linked immunosorbent assay (ELISA), which is a type of immunoassay technique, has been utilized in a wide variety of industries, including the drug discovery, diagnosis, environmental measurement, and food industries. Typically, ELISA comprises 5 steps: (1) fixation of antibodies or antigens (solid-phase formation); (2) binding of target substances; (3) binding of enzyme-labeled antibodies; (4) enzyme reactions; and (5) optical detection (absorption, fluorescence, or luminescence detection). As enzyme labels, horseradish peroxidase, alkaline phosphatase, and the like are used. Among many immunoassay techniques, ELISA is carried out with a particularly high sensitivity. In fact, however, sensitivity is often not as high as expected due to nonspecific adsorption of biomolecules to a solid-phase carrier. In particular, a complex such as an enzyme-labeled antibody is likely to adsorb to a solid-phase carrier, and such adsorption is a primary cause for noise in ELISA. In order to prevent such nonspecific adsorption, a carrier may be blocked with bovine serum albumin (BSA), although the effects thereof are limited. Accordingly, polyethylene glycol (PEG), which effectively prevents nonspecific adsorption of biomolecules, has drawn attention. Specifically, it allows antibodies or antigens to be fixed to a carrier with the aid of PEG linkers, so as to prevent nonspecific adsorption of biomolecules to the solid-phase carrier.
Patent Document 1 discloses a method of fixing an antibody onto a gold surface via a PEG linker. Specifically, a nonionic functional group is introduced onto the gold surface, one end of a heterobifunctional PEG is covalently bound thereto, and an antibody is bound to the other end. Patent Document 1 describes that noise generated by the surface plasmon resonance technique can be reduced to a significant degree with such technique.
Patent Document 2 discloses a technique in which a nucleic acid or protein is fixed onto a glass surface via a PEG linker. Specifically, a silane compound having a PEG linker is synthesized, the resulting compound is applied to a glass surface, and a nucleic acid or protein is bound to an end of the PEG linker. Patent Document 2 describes that the signal-to-noise (S/N) ratio (i.e., sensitivity) of a biochip is improved by such technique.
Patent Document 3 discloses a technique in which a nucleic acid is fixed onto a glass surface via a PEG linker. Specifically, an amino group is introduced onto a glass surface with the aid of a silane coupling agent, one end of a homobifunctional PEG is covalently bound thereto, and a nucleic acid is bound to the other end. Patent Document 3 describes that the sensitivity of a biosensor is improved by such technique.
Meanwhile, various biochemical tests, such as immunoassays, often involve the use of plastic experimental instruments. Because of the hydrophobic properties of plastic materials, the surface of a plastic base material is occasionally modified so as to become a hydrophilic surface, so that the base material can be made suitable for applications requiring hydrophilic properties. For example, corona discharge processing, plasma processing, UV ozonation, electron irradiation, or laser processing can be carried out.